The present invention relates to a method for determining a compaction degree of layers of hot materials, particularly of asphalt, as well as a system for determining a compaction degree and a compacting machine.
In asphalt road construction, it is presently customary to detect the quality of the asphalt compaction by taking a boring sample and analyzing it in a laboratory. This procedure is problematic because the measurement is performed only by way of spot checks and only after termination of the compacting process. It will not be possible to make an assessment of the whole treated surface. The compacting process will be examined only retroactively and cannot be adjusted already during the treatment.
Further, use is made of electronic probes which are manually applied and are capable of detecting a degree of compaction existing on a given spot. Such electronic probes offer the advantage of delivering individual results already while the compacting is still in progress. Also in this measuring method, however, the spot-wise character of the measurements makes it impossible to obtain results on the whole treated surface.
From the field of earthwork engineering, methods for indirect detection of the compaction degree are already known. In these methods, the rigidity value is computed during the compacting movement of the machine on the basis of acceleration signals of the vibrating roll tire and the underlying ground, using mathematical methods for computation. The results will be plotted and directly visualized to the user via a monitor.
To obtain an areal result already during the compacting process, one has meanwhile proceeded—subsequent to the above described method from earthwork engineering—to apply similar methods also in asphalt paving by trying to determine the rigidity of the asphalt. However, the resulting rigidity value of the condensed asphalt is influenced by a large number of factors. Examples worth mentioning among such factors are an inhomogeneous underlying ground, a varying layer thicknesses, patches and the asphalt temperature. Due to these influencing factors, a rigidity measurement is unsuited for a sufficient evaluation of the quality of the compacting work. These methods are thus hardly useful in the context of asphalt compacting.
Therefore, a considerable need exists for a method adapted to optimize the compacting process already during the processing.
From EP Patent 0 698 152 A1, there are already known a method and a device for determining the compaction degree of a ground surface. To perform the determination process, the ground surface to be treated is first divided into unit surface segments. When a pass is made over given unit surface segment, various data of the unit surface segments (e.g. asphalt temperature or speed of the roll) are detected by suitable sensors or measurement devices. On the basis of these data, the compaction degree of the unit surface segment is computed as a partial compaction effect or a partial index number for the segment that is being passed over. The current total compaction value and respectively total index number for a unit surface segment is obtained by adding the current partial compaction effect or partial index number to the total compaction effect or total index number of the preceding pass of this unit surface segment. In this regard, the method is based on the assumption that the compaction degree will increase quasi-logarithmically along with the number of passes.
A disadvantage of this method resides in the idealized division of the to-be-treated ground surface into unit surface segments. Notably, a typical course of a roadway which also curves can thus not be unambiguously represented by this known approach. This also makes it impossible to perform an unambiguous evaluation of the compacting work, particularly in the edge regions of the ground surface to be compacted. A further problem is caused by the fact that, in practice, the moving paths of the compacting machines do not extend linearly side by side but, instead, the ground is to be processed along mutually overlapping paths. Particularly when using a plurality of compacting machines simultaneously, it will neither be possible nor desirable to perform the movements with rigid tracking. As a result, the case may occur that the unit surface segments are only partially passed over by the compacting machines. If, for instance, it happens that a unit surface segment is several times passed over only on one half but is nonetheless evaluated as fully treated, it will be communicated to the driver that the compacting work for this unit surface segment has already been completed although, in the extreme case, half of this unit surface segment has actually been left untreated.
Thus, it is an object of the present invention to provide a method for determining a compaction degree and a system for performing such method which allow for a more-accurate indication of compaction degrees of a surface to be treated while avoiding the above outlined disadvantages of the state of the art.